Refactor weight management in WeightStore to use checked arithmetic for safety. Replace debug assertions with runtime assertions to ensure invariants are maintained during weight updates. This change enhances error handling and prevents potential underflows in total weight calculations during insertions and removals. (#43)

Author: TKorr

src/store/weight.rs

@@ -501,16 +501,17 @@ where
     pub fn try_insert(&mut self, key: K, value: Arc<V>) -> Result<Option<Arc<V>>, StoreFull> {
         let new_weight = self.compute_weight(value.as_ref());
         if let Some(entry) = self.map.get_mut(&key) {
-            debug_assert!(
+            assert!(
                 self.total_weight >= entry.weight,
                 "WeightStore invariant violated: total_weight ({}) is less than entry.weight ({})",
                 self.total_weight,
                 entry.weight
             );
-            let next_total = self
+            let base_total = self
                 .total_weight
-                .saturating_sub(entry.weight)
-                .saturating_add(new_weight);
+                .checked_sub(entry.weight)
+                .expect("WeightStore invariant violated: checked_sub failed after invariant check");
+            let next_total = base_total.checked_add(new_weight).ok_or(StoreFull)?;
             if next_total > self.capacity_weight {
                 return Err(StoreFull);
             }
@@ -525,7 +526,8 @@ where
         if self.map.len() >= self.capacity_entries {
             return Err(StoreFull);
         }
-        if self.total_weight + new_weight > self.capacity_weight {
+        let next_total = self.total_weight.checked_add(new_weight).ok_or(StoreFull)?;
+        if next_total > self.capacity_weight {
             return Err(StoreFull);
         }
 
@@ -536,7 +538,7 @@ where
                 weight: new_weight,
             },
         );
-        self.total_weight += new_weight;
+        self.total_weight = next_total;
         self.metrics.inc_insert();
         Ok(None)
     }
@@ -560,11 +562,14 @@ where
     /// ```
     pub fn remove(&mut self, key: &K) -> Option<Arc<V>> {
         let entry = self.map.remove(key)?;
-        debug_assert!(
+        assert!(
             self.total_weight >= entry.weight,
             "total_weight underflow in remove"
         );
-        self.total_weight = self.total_weight.saturating_sub(entry.weight);
+        self.total_weight = self
+            .total_weight
+            .checked_sub(entry.weight)
+            .expect("WeightStore invariant violated: checked_sub failed after invariant check");
         self.metrics.inc_remove();
         Some(entry.value)
     }